1. Field of the Invention
The present invention relates to an occupant detecting apparatus for detecting an occupant seated on a passenger seat of a vehicle with an airbag.
2. Description of the Related Art
In a vehicle, an airbag is provided in a driver seat in order to alleviate the impact of a collision. Generally, since an adult is seated on the driver seat, when any occupant seated on the driver seat is detected, the inflation of the airbag is always permitted.
On the other hand, an airbag is also provided in a front passenger seat. In this case, since a child or an infant as well as an adult may be seated on the front passenger seat, the permission for the inflation of the airbag depends upon an occupant seated on the front passenger seat. Note that, when a child or an infant is seated on the front passenger seat, if the airbag is inflated, the face of the child or infant is damaged by the inflation of the airbag, which invites a more serious result. Therefore, when a child or an infant is seated on the front passenger seat, the inflation of the airbag is not permissible.
In order to determine whether an occupant seated on the front passenger seat is an adult or a child (infant), occupant detecting apparatuses have been developed. As a result, only when an occupant seated on the front passenger seat is an adult, is the inflation of the airbag permitted to protect a child (infant) from being seriously injured.
A first prior art occupant detecting apparatus is constructed by a load sensor provided on a bottom part of a front passenger seat (see: JP-A-9-207638 and JP-A-10-297334). For example, if the output voltage of the load sensor is higher than a reference value, it is determined that an adult is seat on the front passenger seat. Otherwise, it is determined that a child or an infant is seated on the front passenger seat. Note that it is possible to compare the output voltage of the load sensor with two reference values.
In the above-described first prior art occupant detecting apparatus, however, when a large luggage is seated on the front passenger seat, such a large luggage is considered as an adult to permit the inflation of the airbag. That is, it is impossible to discriminate an adult from a large luggage.
A second prior art occupant detecting apparatus is constructed by electric field sensors (see: JP-A-11-78655). This will be later explained in detail. That is, the electric field sensors can detect a human body, whether it is an adult, a child or an infant.
In the above-described second prior art occupant detecting apparatus, however, the electric field sensors detect a wet seat with no occupant as a human body to permit the inflation of the airbag.
Thus, both of the first and second prior art occupant detecting apparatuses are inferior in the detection accuracy.